Investments (Schedule Of Other Investments) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended				12 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	$ 932,639				$ 911,392
Unfunded Commitments	451,494				467,524
Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	490,658				368,052
Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	441,981				543,340
Hedge Funds [Member] | Investments without redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P30D
Total Fair Value [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	804,505				764,081
Unfunded Commitments	451,494				467,524
Total Fair Value [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	490,658				368,052
Total Fair Value [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	313,847				396,029
Total Fair Value [Member] | Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	266,837				216,825
Unfunded Commitments	451,494				467,524
Total Fair Value [Member] | Private Equity Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	266,837				216,825
Total Fair Value [Member] | Private Equity Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0				0
Total Fair Value [Member] | Private Equity [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	161,667				144,422
Unfunded Commitments	239,697				263,519
Total Fair Value [Member] | Private Equity [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	161,667				144,422
Total Fair Value [Member] | Private Equity [Member] | Investments with redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	2 years		2 years
Total Fair Value [Member] | Private Equity [Member] | Investments with redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	9 years		9 years
Total Fair Value [Member] | Private Equity [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0				0
Total Fair Value [Member] | Mezzanine Debt [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	95,162				64,627
Unfunded Commitments	206,856				198,756
Total Fair Value [Member] | Mezzanine Debt [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	95,162				64,627
Total Fair Value [Member] | Mezzanine Debt [Member] | Investments with redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	5 years		8 years
Total Fair Value [Member] | Mezzanine Debt [Member] | Investments with redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	9 years		9 years
Total Fair Value [Member] | Mezzanine Debt [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0				0
Total Fair Value [Member] | Distressed [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	10,008				7,776
Unfunded Commitments	4,941				5,249
Total Fair Value [Member] | Distressed [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	10,008				7,776
Estimated remaining restriction period	4 years		4 years
Total Fair Value [Member] | Distressed [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0				0
Total Fair Value [Member] | Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	505,176				515,298
Unfunded Commitments	0				0
Total Fair Value [Member] | Hedge Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	223,821				151,227
Total Fair Value [Member] | Hedge Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	281,355				364,071
Total Fair Value [Member] | Distressed Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	165,253				151,227
Unfunded Commitments	0				0
Total Fair Value [Member] | Distressed Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	165,253				151,227
Estimated remaining restriction period	1 year
Total Fair Value [Member] | Distressed Funds [Member] | Investments with redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period			1 year
Total Fair Value [Member] | Distressed Funds [Member] | Investments with redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period			2 years
Total Fair Value [Member] | Distressed Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0				0
Total Fair Value [Member] | Equity Long/Short [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	134,036				99,365
Unfunded Commitments	0				0
Total Fair Value [Member] | Equity Long/Short [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	58,568				0
Estimated remaining restriction period	1 year
Total Fair Value [Member] | Equity Long/Short [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	75,468				99,365
Redemption frequency	Quarterly	[1]			Quarterly	[1]
Total Fair Value [Member] | Equity Long/Short [Member] | Investments without redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P30D	[1]	P30D	[1]
Total Fair Value [Member] | Equity Long/Short [Member] | Investments without redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P60D	[1]	P60D	[1]
Total Fair Value [Member] | Multi-Strategy Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	100,263				136,958
Unfunded Commitments	0				0
Total Fair Value [Member] | Multi-Strategy Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0				0
Total Fair Value [Member] | Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	100,263				136,958
Redemption frequency	Quarterly	[1]			Quarterly	[1]
Total Fair Value [Member] | Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P45D	[1]	P45D	[1]
Total Fair Value [Member] | Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P90D	[1]	P90D	[1]
Total Fair Value [Member] | Event Driven Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets					14,018
Unfunded Commitments					0
Total Fair Value [Member] | Event Driven Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets					0
Total Fair Value [Member] | Event Driven Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets					14,018
Redemption frequency					Annual	[1]
Redemption notice period			P60D	[1]
Total Fair Value [Member] | Relative Value Credit [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	105,624				113,730
Unfunded Commitments	0				0
Total Fair Value [Member] | Relative Value Credit [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0				0
Total Fair Value [Member] | Relative Value Credit [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	105,624				113,730
Redemption frequency	Quarterly	[1]			Quarterly	[1]
Redemption notice period	P60D	[1]	P60D
Total Fair Value [Member] | High Yield Loan Fund [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	32,492				31,958
Unfunded Commitments	0				0
Total Fair Value [Member] | High Yield Loan Fund [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0				0
Total Fair Value [Member] | High Yield Loan Fund [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	32,492				31,958
Redemption frequency	Monthly	[1]			Monthly	[1]
Redemption notice period	P30D	[1]	P30D	[1]
Carrying Value [Member] | Other Private Securities [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	128,134				147,311
Unfunded Commitments	0				0
Carrying Value [Member] | Other Private Securities [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0				0
Carrying Value [Member] | Other Private Securities [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	$ 128,134				$ 147,311

[1] The redemption frequency and notice periods only apply to the investments without redemption restrictions. Some or all of these investments may be subject to a gate as described below.